Pressure treatment of dispersed granules

ABSTRACT

SOLID MATERIALS (E.G. POLYVINVYL CHLORIDE) WHICH ARE GRANULATED AND DISPERSED IN A LIQUID MEDIUM IN WHICH THEY ARE INSOLUBLE (E.G. WATER) ARE SUBMITTED TO A PRESSURE OF AT LEAST 1.5 ATMOSPHERES. THE PRESSURE TREATMENT INCREASES THE BULK DENSITY OF THE GRANULATED SOLID AND RESULTS IN PARTICLES HAVING A SMOOTH SURFACE AND OTHER IMPROVED PROPERTIES.

United States Patent 7 US. Cl. 264117 4 Claims ABSTRACT OF THE DISCLOSURE Solid materials (e.g. polyvinyl chloride) which are granulated and dispersed in a liquid medium in which they are insoluble (e.g. water) are submitted to a pressure of at least 1.5 atmospheres. The pressure treatment increases the bulk density of the granulated solid and results in particles having a smooth surface and other improved properties.

DISCLOSURE OF THE \INVENTION This application is a continuation-in-part of my copending application, Ser. No. 725,271, filed Apr. 26, 1968 now Pat. No. 3,577,489, which in turn is a continuationin-part of my application, Ser. No. 649,088, filed June 26, 1967 now abandoned, which application in turn is a continuation-in-part of my applications, Ser. No. 609,712, filed Jan. 10, 1967 now abandoned, and Ser. No. 631,885, filed Apr. 19, 1967 now abandoned.

This invention relates to the granulation of solid materials. More particularly, this invention relates to the granulation of solids by dispersion of a solution, plastisol, or melt of this solid in a medium in which the solid is not soluble.

Specifically, this invention relates to improvements in processes of granulation by dispersion of a solid material in a liquid in which the solid is not soluble.

A variety of processes are known whereby a solid material can be granulated or finely divided by dispersing the material, solution melt, or gel thereof with stirring in a medium in which the solid is not soluble. Such processes are described, for instance, in U.'S. 3,308,211 and 3,245,- 934.

In my abandoned application mentioned above, Ser. No. 609,712, I disclose a process for granulation. In that process, water insoluble materials such as soaps and pigments are granulated by dispersion and precipitation in Water above 60 C. in the presence of 3 to 25% by weight and preferably 20% by weight of an auxiliary granulation agent. The precipitation is accomplished with stirring of the aqueous medium, the rate of stirring depending upon the particle size and characteristics of granulate desired. In general, higher stirring speeds will give more finely divided granulates and slower speeds will give coarser granulates. The auxiliary agents can be characterized as organic compounds insoluble or only slightly soluble in water with molecular weights above 150, preferably above 200, and having a softening point of below 100 C. The auxiliary agents for granulation contain long chain aliphatic radicals. Among these may be mentioned alcohol esters, fatty acid esters of multivalent alcohols, alkyd esters, ester waxes, fatty acid amides and fatty acid alkyloamides, fatty acid nitriles, alkylphenols, fatty ketone and mixtures of mineral oils and liquid parafiins with metal soaps, fatty acid hydrides, and mixtures which con- ICC tain mineral oil or liquid parafiins and which have a softening point of below C. Among the fatty acid esters, esters of multivalent alcohols, particularly alkylene glycol esters including polyalkylene glycol esters and most particularly ethylene glycol esters, are suitable. Such esters act as not only auxiliary granulating agents, but also give the end product special characteristics such as increased stability.

The granulated materials prepared in accordance with the above-described processes are subsequently removed from the liquid dispersing medium by known methods. It has been found, however, that the granulated materials have certain deficiencies in their properties. One deficiency is low bulk density. Another deficiency is a non-uniform and rough surface on the granulated particles. Another particular deficiency where the granulated material is heavily plasticized resinous material, such as polyvinyl chloride plastisol, is the lack of transparency of the particles. It has now been discovered that these deficiencies can be overcome and the superior granulated product can be obtained by the methods of this invention.

Accordingly, it is an object of this invention to prepare granulated solid materials.

It is another object of this invention to prepare granules of solid materials having high bulk density.

Still another object of this invention is the preparation of solid materials in granulated form, in which the granules have a smooth surface.

Still another object of this invention is the preparation of granulated particles, particularly plasticized polymeric particles, having a higher degree of transparency than normally obtainable by such processes.

Still other objects of this invention will be apparent from the following disclosure.

Briefly, the process of this invention comprises the treatment of a dispersion of a solid material in a liquid medium in which the solid material is substantially insoluble by submission of the dispersed solid to a pressure of at least 1.5 atmospheres. The conditions can be varied widely and depend largely upon the nature of the solid material being granulated.

The process of this invention can be applied to any dispersion of a solid material in a liquid medium in which the solid is substantially insoluble, but the process finds particular application where it is intended that the solid be recovered from the dispersion as a finely divided solid. A particularly valuable area of utility of the present process is in the granulation of polymeric materials. The invention is exemplified below with polyvinyl chloride. Other polymeric or non-polymeric materials can be used.

Polymeric materials which may be granulated in accordance with the improved process of this invention include polyacrylic acids, polymethacrylates and their copolymers, polyvinyl halides, polyvinyl acetates or their copolymers, polyolefins such as polyethylene, polypropylene, or polybutylene, cellulose derivatives, polystyrenes, polyesters, polyamides, or polycarbonates, and various mixtures thereof. In addition to the abovementioned polymeric materials which are thermoplastics, certain of the thermosetting polymeric materials are also suitable, such as phenolic resins, cresol resins, epoxy resins, elastomers such as unvulcanized natural rubber or varieties of synthetic rubber such as acrylonitrile-butadiene-styrene rubbers, acrylonitrile-butadiene rubbers, and polychloroprene. Also useful are resins such as polysiloxanes, polyurethanes, polyethers, and the like. As mentioned above, the dispersion of the solid material and the liquid medium can be prepared by a variety of methods, some of which are already well-known, and which are disclosed, for instance, in US. Patents 3,308,211 and 3,245,934. It is to be emphasized that the dispersion 3 need not be prepared in any special manner, but the present process can be applied to improve the granulates derived from those dispersions.

The pressure treatment step which comprises the essential feature of this invention can be applied while dispersion is taking place, but it is preferred that the pressure step be performed after dispersion has taken place. It has been found that shorter treatment times are necessary when a separate post-dispersion pressure step is utilized. The pressure treatment step is preferably conducted while the dispersion is stirring or being otherwise agitated.

The liquid dispersing medium is preferably water or an aqueous solution but the invention is by no means limited thereto.

This invention is primarily concerned with the improvement of granulates which have been formed by dispersion of a solid material in a liquid medium in which the solid is not substantially soluble. The invention is not, however, limited thereto and can be applied to granulates prepared by other well-known means simply by dispersing the granulates in a liquid in which they are not soluble and by performing the pressure treatment on the dispersion.

The term solid materia as used herein encompasses mixtures which are capable of retaining their shape at ordinary room temperature. For instance, plasticized polymers such as polyvinyl chloride plastisols are specifically intended. The solid material which is granulated may also contain a variety of ingredients such as pigments, fillers, preservatives, lubricants, antistatic agents, anti-flame agents, and the like. These additives can be added prior to granulation. The ingredients are selected, in general, to provide finished, free-flowing granulates having optimum composition for their ultimate use. The composition of the particles is not critical and does not constitute a part of this invention.

The proper heat and pressure can be obtained by known means. It has been found that heating by a high frequency electric field is advantageous in certain instances. The pressure can be autogeneous or can be maintained in other manners. The proper conditions of pressure-temperature and time necessary to achieve the desired results are easily determined. In general, the pressure is above 1.5 atmospheres and preferably in the range of 1.5 to 8.5 atmospheres. The temperature used is normally in the range of 110 to 180 C. corresponding to the temperatures of saturated steam necessary to achieve the above pressures. Lower or higher temperatures can be used depending on the material being granulated. Time of treatment varies with the conditions used, but in general, a time of 20 seconds to 30 minutes is desirable.

The process of this invention can be used to increase the bulk density of granulates prepared in the described manner by to 50% and more as will be shown in the following examples.

This invention may be more fully understood by reference to the following examples. All parts and percentages are by weight unless otherwise indicated. These examples are illustrative of certain specific embodiments designed to teach those skilled in the art how to practice the invention and represent the best mode contemplated for carrying out the invention but are not intended to limit the scope of the invention in any way.

I each of the examples, the dispersed plasticized polyvinyl chloride to be submitted to the process of this invention was obtained by dispersing polyvinyl chloride which had been previously mixed with the plasticizer at a temperature of greater than 60 into rapidly stirring water. The resulting dispersion was then treated as described in the examples.

Example 1 This example illustrates the treatment of plasticized polyvinyl chloride granulate in accordance with the process of this invention.

The following ingredients were granulated in suspension by dispersing polyvinyl chloride dissolved in the plasticizer in water as described above.

Parts Polyvinyl chloride (S=PVC, 70/54) 50.0 Dioctylphthalate 30.0 BCR 02 (barium-cadmium stabilizer) 0.5 BC 12 SL (barium-cadmium stabilizer) 0.1

This example illustrates the treatment vof plasticized polyvinyl chloride granulate in accordance with this invention and illustrates the effect of increasing the pressure treatment time.

The composition and procedure used was as in Example l with the exception that the treatment time was 20 minutes (instead of 10 minutes as in Example 1). The results are summarized in Table I below.

TABLE I Example Control 1 2 Time of pressure treatment (min 0 10 20 Bulk density (g./1.) 365 500 555 Transparency--. None Good Good Surface 1 Wavy. 2 Smooth.

Example 3 This example illustrates the treatment of plasticized polyvinyl chloride containing additional ingredients, pigment, filler, etc. in accordance With this invention.

The procedure used was as in Example 1 with the exception that the time of pressure treatment was 15 minutes and the plasticized polyvinyl chloride granules had the following composition:

. Parts Polyvinyl chloride (S/PVC) 40.00 Diisononylphthalate 17.15 Chalk 9.00 White lead 1.00

Calcium stearate 0.16 Parafiin oil 0.28

The treated granulate was separated and dried. The granulate had a bulk density of 550-560 g./l. compared to 450-460 g./l. for a granulate prepared in the'same manner but not submitted to the pressure treatment. The surface of the pressure treated granulate particles was smooth, while the untreated particles had rough spots.

The composition described above finds particular utility in the production of extruded cable and cable coverings. In extrusion, the pressure-treated material exhibits 25% greater output than the material not pressure treated.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.

What is claimed is:

1. In the process of granulation of solid thermoplastic polymer materials by dispersion and agitation in an aqueous liquid medium in which said solid material is substantially insoluble, the improvement comprising submission of the dispersed solid material to a pressure of 1.5 atmospheres to 8.5 atmospheres at a temperature of 110 to 180 C. for 20 seconds to 30 minutes.

2. The process of claim 1 wherein said thermoplastic polymer is polyvinyl chloride.

3. The process of claim 2 wherein said thermoplastic polymer is plasticized polyvinyl chloride containing 0.10 to 1.0 part by weight based on said polyvinyl chloride of a plasticizer for polyvinyl chloride.

4. 'Ihe process of claim 1 wherein heating is accomplished by means of a high frequency electric field.

References Cited UNITED STATES PATENTS 3,278,661 10/1966 Beck 264--l17 3,366,615 1/1968 Miller 26092.1 3,449,483 6/ 1969 Quist 264-417 JOSEPH L. SCHOFER, Primary Examiner I. A. DONAH'UE, JR., Assistant Examiner U.S. Cl. X.R. 

